Ceramics composition, laminated type ceramics capacitor and production method of ceramics composition

Abstract

To provide a ceramics composition, a laminated type ceramics capacitor used with the same, and a production method of the ceramics composition, which preserve a relatively high dielectric constant (ε≥500) in a wide temperature range (a room temperature to 150°C) and also has a dielectric characteristic with low DC bias dependency.SOLUTION: The present invention relates to a ceramics composition that contains a constituent derived from a base material represented with a chemical formula of Ba(1-x)SrxTi(1-y-z)GayNbzO3, and where x is in a range of 0.01 or more and 0.30 or less, and, for y and z, y+z is in a range of 0.04 or more and 0.20 or less and y / z is in a range of 0.8 or more and 1.2 or less.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a ceramic composition, a multilayer ceramic capacitor using the same, and a method for producing the ceramic composition. [Background technology]

[0002] In recent years, there has been a demand for multilayer ceramic capacitors (MLCCs) with DC bias (direct current voltage)-free dielectric properties as automotive electronic components. Because automotive MLCCs are used under high electric fields, the large electric field and temperature dependence of the dielectric constant of existing MLCCs poses a challenge. Specifically, there is a demand for materials that maintain a relatively high dielectric constant (ε≧500) over a wide temperature range (-55°C to 150°C) while also possessing dielectric properties with low DC bias dependence.

[0003] Materials with high dielectric constants include barium titanate (BaTiO 3、 BaTiO3-based semiconductor ceramics have been proposed in which Ga and Nb simultaneously substitute for the Ti site in BaTiO3 (hereinafter sometimes referred to as "BT") (see, for example, Patent Documents 1 and 2). All of the above material compositions have a high dielectric constant and are ferroelectric materials near room temperature, so the dielectric constant drops significantly when a DC bias is applied, and the DC bias characteristics are insufficient. In contrast, materials that are paraelectric near room temperature have excellent DC bias characteristics, and the dielectric constant does not drop significantly even when a DC bias is applied. However, because they are paraelectric, the dielectric constant tends to be low.

[0004] Furthermore, research based on a chemical grain size model has been reported in which barium titanate (BT) is co-doped with heterogeneous elements Nb-Mn while satisfying the electrical neutrality condition, thereby destroying the long-range order (see Non-Patent Document 1). Although the results of this research achieved DC bias-free dielectric properties, the relative permittivity was not sufficient. Achieving a higher relative permittivity would be expected to lead to a wider range of applications. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-206890 [Patent Document 2] Special Publication No. 2009-509906 [Non-patent literature]

[0006] [Non-Patent Document 1] P. Sapkota et al., Jpn. J. Appl. Phy., 61, SN1023 (2022). Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the inventors focused on barium strontium titanate (hereinafter sometimes referred to as "BST") dielectric ceramics, which has a Curie temperature of around 70°C and a relative dielectric constant greater than that of BT at room temperature. 4+ site) contains a foreign element, Ga 3+ -Nb 5+ By co-doping with , we attempted to develop a new dielectric material with a high dielectric constant that overcomes the electric field and temperature dependence that is prominent in BST.

[0008] The present invention aims to provide a ceramic composition that maintains a relatively high relative dielectric constant (ε≧500) over a wide temperature range (room temperature to 150°C) and has dielectric properties with low DC bias dependency, a multilayer ceramic capacitor using the same, and a method for producing the ceramic composition. [Means for solving the problem]

[0009] In order to achieve the above object, the ceramic composition of the present invention is a ceramic composition having the chemical formula Ba (1-x) Sr x Ti (1-y-z) Ga y Nbz Contains components derived from the base material represented by O3, The x is in the range of 0.10 or more and 0.30 or less, The y+z is in the range of 0.04 or more and 0.20 or less, The y and z are characterized in that y / z is in the range of 0.8 or more and 1.2 or less.

[0010] The ceramic composition of the present invention is also a ceramic material having the chemical formula Ba (1-x) Sr x Ti (1-y-z) Ga y Nb z Contains components derived from the base material represented by O3, The x is in the range of 0.10 or more and 0.30 or less, The y and z are in a range of 0.04 or more and 0.20 or less, wherein y and z are in the range of 0.8 to 1.2, inclusive, with y / z being the ratio of 0.8 to 1.2, A ceramic composition obtained by firing at least the base material and additives, The base material is characterized in that BaCO3, TiO2, SrCO3, and Ga2O3 are subjected to a first calcination by a solid phase method, then mixed with Nb2O5, and further subjected to a second calcination to obtain a calcined powder.

[0011] The multilayer ceramic capacitor of the present invention has a structural element in which layers containing a ceramic composition and internal electrodes are alternately laminated, and the ceramic composition is the ceramic composition of the present invention.

[0012] The method for producing a ceramic composition of the present invention includes a first calcination step of calcining BaCO3, TiO2, SrCO3, and Ga2O3 by a solid phase method to form a first calcined powder; a second calcination step of further calcining the mixture of the first calcined powder and Nb2O5 to form a base material of a ceramic composition; a firing step of firing the base material and the additives to obtain a ceramic composition, The base material has the chemical formula Ba (1-x) Srx Ti (1-y-z) Ga y Nb z It is represented by O3, The x is in the range of 0.10 or more and 0.30 or less, The y and z are in a range of 0.04 or more and 0.20 or less, The y and z are characterized in that y / z is in the range of 0.8 or more and 1.2 or less. [Effects of the Invention]

[0013] The present invention can provide a ceramic composition that maintains a relatively high relative dielectric constant (ε≧500) over a wide temperature range (room temperature to 150°C) and has dielectric properties with low DC bias dependency, a multilayer ceramic capacitor using the same, and a method for producing the ceramic composition. [Brief explanation of the drawings]

[0014] [Figure 1] 1A and 1B are graphs showing the results of XRD (X-ray diffraction) analysis of ceramic compositions according to Examples and Comparative Examples, where Fig. 1A is the graph after the first calcination step, Fig. 1B is the graph after the second calcination step, and Fig. 1C is the graph after the main firing step. [Figure 2] 1 shows SEM images of ceramic compositions according to examples and comparative examples. [Figure 3] 1 is a graph showing the temperature dependence of the relative dielectric constant of ceramic compositions according to Examples and Comparative Examples. [Figure 4] 1 is a graph showing the co-doping amount dependence of the relative dielectric constant at 25° C. and 200° C. for ceramic compositions according to Examples and Comparative Examples. [Figure 5] 5A and 5B are graphs showing DC bias attenuation rates for ceramic compositions according to examples and comparative examples, where (A) is an overall graph including data for y, z = 0 (comparative example), and (B) is an enlarged graph showing data other than y, z = 0. [Figure 6]1 is a graph showing DC bias attenuation rates for ceramic compositions according to examples and comparative examples. [Figure 7] 1 is a graph showing the dielectric properties of ceramic compositions doped with different y / z ratios. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following examples illustrate the forms and configurations of the present invention, but the present invention is not limited to these examples. All examples that comply with the intent of the claims, problem-solving means, effects of the invention, etc. are included in the present invention.

[0016] The ceramic composition of the present invention contains components derived from a matrix of a barium strontium titanate-based compound. The matrix is a compound in which some of the Ti sites of barium strontium titanate are substituted with Ga and Nb, and has the chemical formula Ba (1-x) Sr x Ti (1-y―z) Ga y Nb z O3. Here, "containing components derived from the matrix" means containing components derived from the matrix itself or components that have been modified by post-treatment such as sintering. For example, the ceramic composition may contain grains of the matrix sintered.

[0017] In the above chemical formula, "x" represents the composition ratio of Sr to the total of Ba and Sr. The x is in the range of 0.10 to 0.30, and preferably in the range of 0.20 to 0.30.

[0018] In the above chemical formula, "y" represents the composition ratio of Ga to the total of Ti, Ga, and Nb. Also, in the above chemical formula, "z" represents the composition ratio of Nb to the total of Ti, Ga, and Nb. The above y + z is in the range of 0.04 to 0.20, preferably in the range of 0.04 to 0.12, and more preferably in the range of 0.04 to 0.08. Although the addition of Ga and Nb in small amounts (even when y and z are small) can cause changes in performance, the above ranges are preferable because they can suppress DC bias at high capacitance.

[0019] The ratio of y to z is preferably in the range of 0.8 to 1.2, more preferably 0.9 to 1.1. Excessive Nb (smaller y / z) tends to cause semiconductor formation and a poor (larger) dielectric loss tangent (tanδ). Furthermore, a decrease in Nb (larger y / z) tends to decrease the relative permittivity.

[0020] The ceramic composition may be a ceramic composition obtained by firing a base material and additives. The base material may be a calcined powder obtained by first calcining BaCO3, SrCO3, TiO2, and Ga2O3 by a solid-phase method, mixing the mixture with Nb2O5, and then calcining the mixture for a second time.

[0021] The ceramic composition may include Ba (1-x) Sr x Ti (1-y―z) Ga y Nb z The grains may include grains derived from a matrix represented by O3. The grains may not have a core-shell structure.

[0022] The absence of a core-shell structure means that the grain does not have a core portion and a shell portion formed by portions having different compositions, and for example, when the grain has a homogeneous structure as described below, it can be said that the grain does not have a core-shell structure. The presence or absence of the core-shell structure can be confirmed, for example, by observing the grain with a STEM or an SEM.

[0023] The grains may have a homogeneous structure, where the elemental concentrations of the components contained in the grains are the same throughout the grains, or the variation in the elemental concentrations within the grains is so small that it can be practically ignored.

[0024] The auxiliary components used in producing the ceramic composition are not particularly limited. The ceramic composition may contain, as auxiliary components, barium compounds, manganese compounds, vanadium compounds, magnesium compounds, calcium compounds, silicon compounds, etc. Examples of barium compounds include barium oxide (BaO), barium carbonate (BaCO3), and barium chloride (BaCl2). Examples of manganese compounds include manganese oxides (MnO2, Mn2O3, Mn3O4), etc. Examples of vanadium compounds include vanadium pentoxide, etc. Examples of magnesium compounds include magnesium oxide (MgO), etc. Examples of calcium compounds include calcium carbonate (CaCO3), etc. Examples of silicon compounds include silicon oxide (SiO2), etc.

[0025] Examples of composition ranges for these minor components are described below. For example, the barium compound (total amount if two or more types are used) may be used in an amount of 0.1 mol to 4.0 mol in Ba equivalent per 100 mol of base material. The manganese compound (total amount if two or more types are used) may be used in an amount of 0.01 mol to 0.5 mol in Mn equivalent per 100 mol of base material. The magnesium compound (total amount if two or more types are used) may be used in an amount of 0.1 mol to 2.0 mol in Mg equivalent per 100 mol of base material. The vanadium compound (total amount if two or more types are used) may be used in an amount of 0.01 mol to 3.0 mol in V equivalent per 100 mol of base material.

[0026] The form of the ceramic composition of the present invention is not particularly limited. The ceramic composition can be in the form of a plate, a sphere, a pellet, or the like. It can also be in a composite form that combines these forms.

[0027] The ceramic composition of the present invention is characterized by having a high relative dielectric constant and a small temperature change in the relative dielectric constant at room temperature to 150° C. Furthermore, the variation in the relative dielectric constant is small even when a DC bias is applied, and the ceramic composition can overcome the electric field dependency.

[0028] [Method for producing ceramic composition] The ceramic composition of the present invention is produced, for example, by the following two-stage calcination process: However, the method for producing the ceramic composition of the present invention is not limited to this.

[0029] (Step 1) A first calcination step in which BaCO3, TiO2, SrCO3 and Ga2O3 are calcined by a solid phase method to form a first calcined powder. (Step 2) A second calcination step in which a mixture of the first calcined powder obtained in the first calcination step (Step 1) and Nb2O5 is further calcined to form a base material of a ceramic composition. (Step 3) A firing step in which the base material and additives obtained in the second calcination step (Step 2) are fired to obtain a ceramic composition.

[0030] At this time, the base material is Ba (1-x) Sr x Ti (1-y-z) Ga y Nb z The compound may be represented by the formula O3 and may be a barium strontium titanate-based compound having a perovskite structure. In the base material, some of the Ti sites of the barium strontium titanate may be substituted with Ga and Nb. It is sufficient that x is in the range of 0.10 to 0.30, and that y + z is in the range of 0.04 to 0.20. Furthermore, it is sufficient that y and z are in the range of y / z is in the range of 0.8 to 1.2.

[0031] Each step will be described in detail below. (Step 1) First calcination step In this step, BaCO3, TiO2, SrCO3, and Ga2O3 are calcined to form a first calcined powder. BaCO3, TiO2, SrCO3, and Ga2O3 may be weighed and mixed as raw materials, and the mixture may be heat-treated (calcined) using a solid-phase method. The amounts of BaCO3, TiO2, SrCO3, and Ga2O3 are adjusted so that the "x" of the base material obtained in the second calcination step (step 2) is in the range of 0.10 to 0.30, and "y + z" is in the range of 0.04 to 0.20. When producing using a solid-phase method, for example, BaCO3, TiO2, SrCO3, and Ga2O3 may be wet-mixed in a solvent. After drying, the mixture may be coarsely crushed and calcined to form a first calcined powder.

[0032] The solvent used in the wet mixing is not particularly limited. For example, water, alcohol solvents, glycol solvents, ketone solvents, ester solvents, ether solvents, aromatic solvents, or a combination of two or more thereof can be used. Examples of alcohol solvents include ethanol, methanol, benzyl alcohol, and methoxyethanol. Examples of glycol solvents include ethylene glycol and diethylene glycol. Examples of ketone solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Examples of ester solvents include butyl acetate, ethyl acetate, carbitol acetate, and butyl carbitol acetate. Examples of ether solvents include methyl cellosolve, ethyl cellosolve, butyl ether, and tetrahydrofuran. Examples of aromatic solvents include benzene, toluene, and xylene.

[0033] The amount of solvent used is preferably 0.5 to 10 times the total mass (total mass) of BaCO3, TiO2, SrCO3, and Ga2O3. The amount of solvent used is more preferably 0.7 to 5 times. Within the above range, BaCO3, TiO2, SrCO3, and Ga2O3 are thoroughly mixed.

[0034] For wet mixing, a wet ball mill or an agitator mill can be used. When using a wet ball mill, a large number of zirconia balls with a diameter of 0.1 mm to 10 mm can be used. The mixing time for wet mixing can be, for example, 8 hours to 48 hours, preferably 10 hours to 24 hours.

[0035] The calcination temperature is preferably 600°C or higher and 1200°C or lower, more preferably 700°C or higher and 1150°C or lower, and even more preferably 700°C or higher and 1100°C or lower.

[0036] The top-keep time of the calcination is not particularly limited, but is preferably from 1 hour to 5 hours, more preferably from 1 hour to 3 hours. The firing atmosphere is also not particularly limited, and examples thereof include vacuum, air, and inert gas atmospheres such as nitrogen and argon.

[0037] As other firing conditions, a temperature rise rate of 50° C. / hour or more and 500° C. / hour or less is preferable, and a temperature rise rate of 70° C. / hour or more and 200° C. / hour or less is more preferable.

[0038] (Step 2) Second calcination step In this step, the mixture of the first calcined powder obtained in (Step 1) and Nb2O5 is further calcined to form a ceramic composition base material. The first calcined powder and Nb2O5 may be weighed and mixed, and the mixture may be heat-treated (calcined) by a solid-phase method. The amount of Nb2O5 is adjusted so that the "y + z" of the base material obtained in the second calcination step is in the range of 0.04 to 0.20. When producing by the solid-phase method, for example, the first calcined powder and Nb2O5 may be wet-mixed in a solvent. After drying, the mixture may be coarsely pulverized and calcined to form a second calcined powder.

[0039] The solvent used in the wet mixing is not particularly limited. For example, water, alcohol solvents, glycol solvents, ketone solvents, ester solvents, ether solvents, aromatic solvents, or a combination of two or more thereof can be used. Examples of alcohol solvents include ethanol, methanol, benzyl alcohol, and methoxyethanol. Examples of glycol solvents include ethylene glycol and diethylene glycol. Examples of ketone solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Examples of ester solvents include butyl acetate, ethyl acetate, carbitol acetate, and butyl carbitol acetate. Examples of ether solvents include methyl cellosolve, ethyl cellosolve, butyl ether, and tetrahydrofuran. Examples of aromatic solvents include benzene, toluene, and xylene.

[0040] The amount of solvent used is preferably 0.5 to 10 times the total mass (total mass) of the first calcined powder and Nb2O5. The amount of solvent used is more preferably 0.7 to 5 times. Within the above range, the first calcined powder and Nb2O5 are thoroughly mixed.

[0041] For wet mixing, a wet ball mill or an agitator mill can be used. When using a wet ball mill, a large number of zirconia balls with a diameter of 0.1 mm to 10 mm can be used. The mixing time for wet mixing can be, for example, 8 hours to 48 hours, preferably 10 hours to 24 hours.

[0042] The calcination temperature is preferably 600° C. or higher and 1200° C. or lower, more preferably 700° C. or higher and 1150° C. or lower, and even more preferably 700° C. or higher and 1100° C. If the calcination temperature is within the above range, sintering proceeds sufficiently, which is preferable in that the obtained base material has few defects.

[0043] The top-keep time of the calcination is not particularly limited, but is preferably from 1 hour to 5 hours, more preferably from 1 hour to 3 hours. The firing atmosphere is also not particularly limited, and examples thereof include vacuum, air, and inert gas atmospheres such as nitrogen and argon.

[0044] Other firing conditions include a temperature rise rate of preferably 50° C. / hour or more and 500° C. / hour or less, more preferably 70° C. / hour or more and 200° C. / hour or less.

[0045] (Step 3) Main firing step In this step, the base material and additives obtained in (Step 2) are fired to obtain a ceramic composition. The mixture obtained by mixing the base material and additives obtained in (Step 2) may be molded, and the molded body may be fired.

[0046] First, the base material obtained in (Step 2) and additives may be wet-mixed in a solvent. The components of the ceramic composition of this embodiment are wet-mixed in a solvent to produce a slurry. The additives may include subcomponents of the ceramic composition, binders, plasticizers, dispersants, etc. The additives may also include lubricants, antistatic agents, etc.

[0047] The solvent used in the wet mixing is not particularly limited. For example, water, alcohol solvents, glycol solvents, ketone solvents, ester solvents, ether solvents, aromatic solvents, or a combination of two or more thereof can be used. Examples of alcohol solvents include ethanol, methanol, benzyl alcohol, and methoxyethanol. Examples of glycol solvents include ethylene glycol and diethylene glycol. Examples of ketone solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Examples of ester solvents include butyl acetate, ethyl acetate, carbitol acetate, and butyl carbitol acetate. Examples of ether solvents include methyl cellosolve, ethyl cellosolve, butyl ether, and tetrahydrofuran. Examples of aromatic solvents include benzene, toluene, and xylene. Among these, alcohol solvents and aromatic solvents are preferred. These solvents have good solubility and dispersibility for various additives contained in the slurry. The alcohol solvent is preferably a low-boiling point solvent such as methanol or ethanol. The aromatic solvent is preferably a low-boiling point solvent such as toluene. The above solvents may be used alone or in any combination and ratio of two or more. When two or more solvents are mixed, the above alcohol solvent and aromatic solvent are preferably mixed.

[0048] The amount of solvent used is preferably 0.5 to 10 times the total mass (total mass) of the base material and additives. The amount of solvent used is more preferably 0.7 to 5 times. Within the above range, the base material, additives, etc. can be thoroughly mixed. Furthermore, the subsequent operation of removing the solvent can be easily performed.

[0049] The binder that can be contained in the slurry is not particularly limited. Examples include polyvinyl alcohol (PVA), polyvinyl butyral (PVB), acrylic resin, etc. The above binders may be used alone or in combination of two or more.

[0050] The amount of binder used is not particularly limited. Preferably, the amount of binder is 0.01% by mass or more and 20% by mass or less based on the total mass (total mass) of the base material and additives. More preferably, the amount of binder is 0.5% by mass or more and 15% by mass or less. By using this range, the density of the molded body is improved.

[0051] The plasticizer that can be included in the slurry is not particularly limited. Examples include phthalate-based plasticizers such as dioctyl phthalate (DOP), benzyl butyl phthalate, dibutyl phthalate, dihexyl phthalate, di(2-ethylhexyl) phthalate (DEHP), and di(2-ethylbutyl) phthalate; adipic acid-based plasticizers such as dihexyl adipate and di(2-ethylhexyl) adipate (DOA); glycol-based plasticizers such as ethylene glycol, diethylene glycol, and triethylene glycol; and glycol ester-based plasticizers such as triethylene glycol dibutyrate, triethylene glycol di(2-ethylbutyrate), and triethylene glycol di(2-ethylhexanoate). Among these, phthalate-based plasticizers such as dioctyl phthalate, dibutyl phthalate, and di(2-ethylhexyl) phthalate are preferred. The use of a phthalate-based plasticizer improves the flexibility of the green sheet produced from the slurry. The above plasticizers may be used alone or in combination of two or more kinds.

[0052] The amount of plasticizer used is not particularly limited. Preferably, the amount of plasticizer is 5% by mass or more and 50% by mass or less, based on the total mass of the binder to be added. More preferably, the amount of plasticizer is 10% by mass or more and 50% by mass or less. Particularly preferably, the amount of plasticizer is 15% by mass or more and 30% by mass or less. By setting the amount within the above range, a sufficient effect as a plasticizer can be obtained.

[0053] The dispersant that can be contained in the slurry is not particularly limited. Examples include phosphate ester-based dispersants and polycarboxylic acid-based dispersants. Among these, phosphate ester-based dispersants are preferred. The dispersants may be used alone or in combination of two or more.

[0054] The amount of dispersant used is not particularly limited. Preferably, the amount of dispersant is 0.1% by mass or more and 5% by mass or less relative to the total mass (total mass) of the base material and additives. More preferably, the amount of dispersant is 0.3% by mass or more and 3% by mass or less. Even more preferably, the amount of dispersant is 0.5% by mass or more and 1.5% by mass or less. By using the amount within the above ranges, a sufficient effect as a dispersant can be obtained.

[0055] As a method of wet mixing, a wet ball mill, an agitator mill, or a bead mill can be used. The wet ball mill may use a large number of zirconia balls with a diameter of 0.1 mm to 10 mm. The mixing time of the wet mixing may be, for example, 8 hours to 48 hours. Preferably, the mixing time is 10 hours to 24 hours.

[0056] Next, the slurry is molded to obtain a molded body of a predetermined size and shape. The molded body may be a sheet. For example, the slurry is molded into a sheet by a doctor blade method or a die coater method. The obtained sheets are then laminated and heat-press molded. If necessary, the molded body may be cut into a desired shape such as a chip shape. This results in a so-called green sheet.

[0057] The thickness of the green sheet (thickness after drying) is not particularly limited. Preferably, the thickness of the green sheet is 30 μm or less. More preferably, the thickness of the green sheet is 20 μm or less. On the other hand, there is no particular lower limit to the thickness of the green sheet (thickness after drying). The thickness of the green sheet is substantially 0.5 μm or more.

[0058] The green sheets may be laminated to a desired thickness and then thermocompression bonded. The conditions for thermocompression bonding are not particularly limited. The temperature during thermocompression bonding is preferably 50°C or higher and 150°C or lower. The pressure during thermocompression bonding is preferably 10 MPa or higher and 200 MPa or lower. The pressing time is preferably 1 minute or higher and 30 minutes or lower. Examples of thermocompression bonding methods include warm isostatic pressing (WIP).

[0059] The stack of green sheets is then cut, thereby producing a green chip having a desired chip shape.

[0060] The binder components and the like contained in the obtained green sheet (or green chip) are preferably removed by thermal decomposition (degreasing treatment). The conditions for the degreasing treatment depend on the type of binder used, but are not particularly limited. Preferably, the degreasing is performed at a temperature of 180°C or higher and 450°C or lower. The degreasing treatment time is not particularly limited. Preferably, the degreasing treatment time is 0.5 hours or higher and 24 hours or lower. The degreasing treatment is performed in air or in an inert gas such as nitrogen or argon. From the viewpoint of ease of process control, the degreasing treatment is preferably performed in air.

[0061] The firing is carried out, for example, by the following method. The compact after the binder removal treatment is subjected to firing. The firing temperature may be 1400°C or lower. The lower limit of the firing temperature is not particularly limited. Preferably, the lower limit is 1000°C or higher. More preferably, the lower limit is 1150°C or higher. The firing temperature range is more preferably 1200°C or higher and 1400°C or lower. Particularly preferably, the temperature range is 1230°C or higher and 1360°C or lower. The firing top-keep time is not particularly limited, but may be 1 hour or higher and 5 hours or lower. Preferably, the firing top-keep time is 1 hour or higher and 3 hours or lower. The temperature rise condition may be 50°C / h or higher and 500°C / h or lower. Preferably, the temperature rise condition is 70°C / h or higher and 200°C / h or lower. The firing atmosphere is not particularly limited. It may be an inert gas atmosphere or a reducing atmosphere. The reducing atmosphere may be a mixture of an inert gas with hydrogen and / or water vapor.

[0062] [Applicable objects of ceramic compositions] The ceramic composition of this embodiment can be used in various electronic components. In particular, the ceramic composition is suitable for use in electronic components that require reliability at high temperatures (e.g., 100°C or higher). One example of an electronic component is a capacitor containing the ceramic composition as a dielectric. Another example is a multilayer ceramic capacitor (MLCC) containing the ceramic composition as a dielectric.

[0063] These electronic components are used, for example, on or near the power module substrate of an electric vehicle, and require high performance and reliability. For example, they are used in power modules equipped with SiC semiconductors. MLCCs containing the ceramic composition can be manufactured, for example, by the following method.

[0064] First, a conductive paste for internal electrodes is printed on the green sheet obtained in the above (Step 3). The printing method may be, for example, screen printing. The conductive paste for internal electrodes may be made of Cu, Ni, Pt, Pd, Ag, or the like. A laminate is formed by stacking a plurality of green sheets on which the conductive paste for internal electrodes has been printed.

[0065] Next, the laminate is sandwiched between green sheets on which no conductive paste for the internal electrodes is printed. The laminate is then pressed together. The laminate is then cut as needed to form green chips. The green chips are then debindered and fired to obtain capacitor chip bodies. The firing conditions may be the same as those described above (Step 3). The resulting capacitor chip bodies may be further annealed during firing in a reducing atmosphere, which allows for reoxidation of the dielectric layers.

[0066] Next, each end face of the internal electrode exposed from the end face of the capacitor chip body is connected to an external electrode. For example, the external electrodes may be formed by applying a conductive paste for the external electrodes to the end faces. The conductive paste for the external electrodes may be any of the materials listed for the conductive paste for the internal electrodes. Alternatively, the paste may be made of alloys such as Cu, Ag, Ag-10Pd, and Ag-coated Cu, and / or carbon materials such as graphite. If necessary, a coating layer may be formed on the capacitor chip body by plating or other processes.

[0067] An example of an electronic component is a multilayer ceramic capacitor. However, the electronic component according to this embodiment is not limited to this. For example, various other components may be used, such as a high-frequency module, an electronic component for a thermistor, or a composite component thereof. [Example]

[0068] EXAMPLES Next, the present invention will be specifically explained with reference to examples and comparative examples, but these do not limit the present invention in any way.

[0069] Ba(1-x) Sr x Ti (1-y―z) Ga y Nb z Powders with the following compositions were prepared: O3 (x = 0.2, y + z = 0, 0.04, 0.08, 0.12, 0.16, 0.20). These powders, except for y + z = 0, were prepared using the two-step calcination method described above.

[0070] The raw materials used were commercially available powders of BaCO3 (Rare Metallic Co., Ltd., 99.99%), SrCO3 (Fujifilm Wako Pure Chemical Corporation, 99.9%), TiO2 (Mitsuwa Chemical Co., Ltd., 99.9%), Ga2O3 (Rare Metallic Co., Ltd., 99.99%), and Nb2O5 (Rare Metallic Co., Ltd., 99.9%). The moisture content of these powders was measured by thermogravimetric analysis and corrected for using the moisture content at the time of weighing.

[0071] Example 1 BaCO3, TiO2, SrCO3, and Ga2O3 were weighed using an electronic balance so that x = 0.2, y = 0.02, and z = 0.02. Pure water was added to the weighed materials to achieve a solids concentration of 33 wt%. Then, wet mixing was performed for 16 hours using a rotating ball mill. 3mm diameter ZrO2 balls were used for the rotating ball mill. The slurry was then removed and dried in a vat at 100°C in the air. The resulting dried powder was coarsely pulverized using a pestle and mortar. The resulting powder was calcined in the air in an alumina crucible (first calcination step). Calcination was performed at 1000°C for 5 hours (heating at 100°C / hour).

[0072] Nb2O5 was weighed using an electronic balance to achieve x = 0.2, y = 0.02, and z = 0.02, and then added to the obtained first calcined powder. Pure water was then added to achieve a solids concentration of 33 wt%. This was followed by wet mixing for 16 hours using a rotary ball mill. 3mm diameter ZrO2 balls were used for the rotary ball mill. The slurry was then removed and dried in a vat at 100°C in the air. The resulting dried powder was coarsely pulverized using a pestle and mortar. The resulting powder was calcined in the air in an alumina crucible (second calcination step). Calcination was performed at 1000°C for 5 hours (heating at 100°C / hour).

[0073] The resulting second calcined powder was coarsely pulverized using a pestle and mortar, a binder (PVB, 3 wt%) was added, and the mixture was pressed at approximately 250 MPa using a uniaxial press to form pellets with a diameter of 10 mm. The resulting pellets were subjected to a binder removal treatment at 700°C for 10 hours. They were then sintered at 1400°C for 5 hours (heating rate: 100°C / hour) (main firing step) to obtain a ceramic composition.

[0074] Example 2 A ceramic composition was prepared under the same conditions as in Example 1, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.04, and z=0.04.

[0075] Example 3 A ceramic composition was produced under the same conditions as in Example 1, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.06, and z=0.06.

[0076] Example 4 A ceramic composition was produced under the same conditions as in Example 1, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.08, and z=0.08.

[0077] Example 5 A ceramic composition was prepared under the same conditions as in Example 1, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.10, and z=0.10.

[0078] (Comparative Example 1) BaCO3, TiO2, and SrCO3 were weighed using an electronic balance so that x = 0.2, y = 0, and z = 0. Pure water was added to the weighed materials to achieve a solids concentration of 33 wt%. Then, wet mixing was performed for 16 hours using a rotating ball mill. 3mm diameter ZrO2 balls were used for the rotating ball mill. The slurry was then removed and dried in a vat at 100°C in the air. The resulting dried powder was coarsely ground using a pestle and mortar. The resulting powder was calcined in the air in an alumina crucible. Calcination was performed at 1000°C for 5 hours (heating at 100°C / hour). The calcined powder was coarsely ground using a pestle and mortar, and XRD measurements were performed.

[0079] [evaluation] The ceramic compositions obtained in the above Examples and Comparative Examples were evaluated as follows.

[0080] (1) Relative density The density of the sintered ceramic composition was measured by the Archimedes method. 0.8 Sr 0.2 The theoretical density of Ti is 5.83 g cm -3 The relative density was calculated using the formula: The relative density of the obtained ceramic compositions was all 95% or more.

[0081] (2)XRD analysis XRD analysis was performed on the ceramic compositions obtained in the examples and comparative examples. CuKα radiation was used as the X-ray source for the XRD analysis. Figure 1 shows the XRD measurement results for each co-doping amount (A) after the first calcination step, (B) after the second calcination step, and (C) after the main firing step. Although impurities were observed during calcination, the sintered samples were confirmed to be single-phase perovskite. Furthermore, while BST alone (without Ga or Nb doping) has a tetragonal structure, the ceramic compositions containing 2 mol% to 10 mol% Ga and Nb (Examples 1 to 5, y = 0.02 to 0.10, z = 0.02 to 0.10) were all attributable to a cubic structure.

[0082] (3) SEM observation The cross sections of the ceramic compositions obtained in the examples and comparative examples were observed using an electron microscope. The sintered ceramics (ceramic compositions) were cut and polished to obtain 2 x 2 x 0.4 mm plate samples. These were then annealed at 1100°C for 4 hours to repair surface damage caused by cutting and polishing. Figure 2 shows SEM images of the surfaces of the sintered ceramics with various co-doping levels. While BST alone is composed of coarse grains of 100 μm, the grain size decreased with increasing co-doping levels, and the sample containing 10 mol% Ga and Nb (y = 0.10, z = 0.10) exhibited grain sizes of less than 1 μm.

[0083] (4) Temperature dependence of dielectric properties The dielectric properties were measured after gold sputtering on the top and bottom surfaces of the plate samples and heating them at 300°C for 10 minutes. The temperature dependence of the dielectric properties was measured at 1 MHz using an LCR meter (Wayne Kerr Electronics, 6440B). Figure 3 shows the temperature dependence of the dielectric constant for each co-doping amount, and Figure 4 shows the dependence of the relative dielectric constant on the co-doping amount at 25°C and 200°C. The dielectric constant decreased with increasing co-doping amount, and the difference in the dielectric constant between 25°C and 200°C also decreased.

[0084] (5) Temperature dependence of dielectric properties PE measurements were performed using a ferroelectric measuring device at 25°C, 10Hz, and 50kVcm.-1 The dielectric constant was measured at 4 mol% Ga and Nb (y = 0.04, z = 0.04), -27.0% at 6 mol% Ga and Nb (y = 0.06, z = 0.06), -18.8% at 8 mol% Ga and Nb (y = 0.08, z = 0.08), and -8.1% at 10 mol% Ga and Nb (y = 0.10, z = 0.10). As a result, we were able to develop a ceramic composition with a DC bias dependency of -33.8% at a relative dielectric constant of 1,400 and -27.0% at a relative dielectric constant of 1,000. In addition, the temperature dependency was relatively flat in the range of 6 to 10 mol%.

[0085] [y / z ratio] Examples 6 to 9 and Comparative Examples 2 to 7 are examples of ceramic compositions prepared by doping Example 2 (x=0.2, y=0.04, z=0.04) with y+z constant (=0.08) and y / z ratios in the range of 0.5 to 1.5.

[0086] (Comparative Example 2) A ceramic composition was prepared under the same conditions as in Example 2, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.027, and z=0.053 (y / z=0.5).

[0087] (Comparative Example 3) A ceramic composition was prepared under the same conditions as in Example 2, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.030, and z=0.050 (y / z=0.6).

[0088] Comparative Example 4 A ceramic composition was prepared under the same conditions as in Example 2, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.033, and z=0.047 (y / z=0.7).

[0089] Example 6 A ceramic composition was prepared under the same conditions as in Example 2, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.036, and z=0.044 (y / z=0.8).

[0090] Example 7 A ceramic composition was prepared under the same conditions as in Example 2, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.038, and z=0.042 (y / z=0.9).

[0091] Example 8 A ceramic composition was produced under the same conditions as in Example 2, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.042, and z=0.038 (y / z=1.1).

[0092] Example 9 A ceramic composition was produced under the same conditions as in Example 2, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.044, and z=0.036 (y / z=1.2).

[0093] (Comparative Example 5) A ceramic composition was prepared under the same conditions as in Example 2, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.045, and z=0.035 (y / z=1.3).

[0094] (Comparative Example 6) A ceramic composition was prepared under the same conditions as in Example 2, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.047, and z=0.033 (y / z=1.4).

[0095] (Comparative Example 7) A ceramic composition was prepared under the same conditions as in Example 2, except that BaCO3, TiO2, SrCO3, Ga2O3, and Nb2O5 were weighed out so that x=0.2, y=0.048, and z=0.032 (y / z=1.5).

[0096] FIG. 7 shows the dielectric properties of Example 2, Examples 6 to 9, and Comparative Examples 2 to 7. It can be seen that tan δ increases when y / z is outside the range of 0.8 to 1.2. The increase in the relative dielectric constant (εr) outside this range is due to the composition becoming semiconducting due to oxygen vacancies. Within this range, the relative dielectric constant decreases due to the precipitation of low εr compositions at the grain boundaries.

[0097] The ceramic composition according to the present embodiment has excellent DC bias characteristics. That is, a multilayer ceramic capacitor using the ceramic composition according to the present embodiment has little change in dielectric constant and no decrease in capacitance even when a DC voltage is applied, thereby realizing high capacitance characteristics.

Claims

1. Chemical formula: Ba （１－ｘ） Sr ｘ Ti （１－ｙ－ｚ） Ga ｙ Nb ｚ O ３ Contains components derived from the base material represented by The x is in the range of 0.10 or more and 0.30 or less, The y and z are in a range of 0.04 or more and 0.20 or less, A ceramic composition, characterized in that y and z are in a range of 0.8 or more and 1.2 or less, in terms of y / z.

2. Chemical formula: Ba （１－ｘ） Sr ｘ Ti （１－ｙ－ｚ） Ga ｙ Nb ｚ O ３ Contains components derived from the base material represented by The x is in the range of 0.10 or more and 0.30 or less, The y and z are in a range of 0.04 or more and 0.20 or less, wherein y and z are in a range of 0.8 to 1.2, and y / z is in a range of 0.8 to 1.

2. A ceramic composition obtained by firing at least the base material and additives, The base material is BaCO ３ , TiO ２ , SrCO ３ and Ga ２ O ３ After the first calcination by the solid phase method, Nb ２ O ５ and then subjecting the mixture to a second calcination to obtain a calcined powder, which is used as a base material.

3. a structural element in which layers containing a ceramic composition and internal electrodes are alternately stacked, 3. A multilayer ceramic capacitor, wherein the ceramic composition is the ceramic composition according to claim 1 or 2.

4. BaCO ３ , TiO ２ , SrCO ３ and Ga ２ O ３ a first calcination step of calcining the mixture by a solid phase method to form a first calcined powder; The first calcined powder and Nb ２ O ５ a second calcination step of further calcining the mixture to form a ceramic composition base material; a firing step of firing the base material and the additives to obtain a ceramic composition, The base material has the chemical formula Ba （１－ｘ） Sr ｘ Ti （１－ｙ－ｚ） Ga ｙ Nb ｚ O ３ is expressed as The x is in the range of 0.10 or more and 0.30 or less, The y and z are in a range of 0.04 or more and 0.20 or less, A method for producing a ceramic composition, wherein y and z are in a range of 0.8 to 1.2, inclusive, in terms of y / z.

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